amplifiers are part of the distortion equation. especially the amplifier<->speaker relationship. if the amplifiers have headroom in the ability to keep the speaker linear, then the subtle ambient clues and musical threads that occupy the soundstage can be fully rendered. obviously acoustics play their role too. it’s not just the amp<->speaker by themselves.
if the amplifier cannot fully control the speaker then the details of the music break down and the soundstage becomes a mess to one degree or another. you are suddenly hearing individual speakers as sound, individual drivers as sound, and not as a musical whole. it’s the distortion that is causing the music to turn to just sound. the distortion reminds us that it’s reproduced, and not real.
this is the biggest cause of the music sounding hard or flat, or the soundstage collapsing. lack of cohesion between the amps and the speakers.
when you hear a system that can do large scale music with ease, when the music breathes, and can keep together and rise and fall with the musical flow, the amplifier has to be right as part of the package. it’s the ’heart’ of what you are hearing. for a recording to be presented completely the amps have to be right.
mono blocks in and of themselves are not significant. there are stereo amplifiers at the highest levels of amplifiers. however; mono blocks can deliver more performance within some design approaches as then you have each channel optimized. but mono blocks or stereo chassis does not tell you good, better, best by itself. too many degrees of good.